Field-effect transistors (FETs) based on strained heterojunction channels have shown significant promise for increased drive current and higher frequency operation, in comparison to traditional FETs with relaxed silicon channels. Strained heterojunction channels are fabricated from materials such as silicon (Si), silicon-germanium (SiGe), germanium (Ge), etc. Forming high-quality electrical contacts is difficult when the source and drain regions of a FET include materials other than pure silicon. High quality contacts to silicon-based FETs are traditionally achieved through a silicide process, where a metal such as cobalt or titanium is alloyed with silicon to form the contact. This process is typically not as effective with semiconductor materials other than silicon. For example, a cobalt silicide contact formed to a source disposed in a strained Si layer and an underlying SiGe layer may form a high-resistivity compound in the SiGe layer, thereby compromising the functionality of the contact. More specifically, discrete regions of cobalt silicide may form in the SiGe layer, with Ge excluded from the cobalt silicide.